Beijing, Hangzhou, Shenzhen, and Chongqing. For each city, a total of 4337 hourly AQI records from January 1, 2024, to June 29, 2024, were selected. In Beijing, the primary observation point was the Tiantan observatory, with auxiliary observation points at Wanshouxigong, Guanyuan, and Olympic Sports Center. Similarly, in Hangzhou, the main observation point was the City Government Building, and auxiliary observation points were Binjiang, Xisha, and Yunqi. In Shenzhen, the main observation point was Longgang, with auxiliary observation points at Overseas Chinese Town, Guanlan, and Xixiang.